JP3408250B2 - Lithium secondary battery - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to improvement of an electrolyte for a lithium secondary battery using a carbon material containing graphite as a single component or a main component as a negative electrode material.

[0002]

2. Description of the Related Art Recently, in recent years,
As a negative electrode material for a lithium secondary battery, a carbon material has been studied as a negative electrode material that replaces the conventional lithium alloy because it has excellent flexibility and there is no risk of electrodeposition of mossy lithium.

By the way, the carbon material that has been mainly studied in the past is coke, and graphite has been almost excluded from the subject of the study. However, in coke, since the amount of lithium inserted is not sufficiently large, it is difficult to obtain a large-capacity battery. As far as the inventors of the present invention know, as a document proposing a secondary battery using graphite as a negative electrode material, USP No.
Only 4,423,125 can be mentioned.

In the above-mentioned US Patent Publication, a carbon material capable of occluding lithium as an active material is used as a negative electrode material, and 1,3-dioxolane as a solvent and LiAsF ₆ as an electrolyte solute are dissolved in an electrolytic solution. A secondary battery using the above has been proposed, and the publication discloses that a secondary battery having excellent cycle characteristics can be obtained.

However, in the embodiment described later,
As shown in the characteristics of the conventional battery, the conventional secondary battery has not only cycle characteristics (cycle life), but also capacity per unit weight of graphite (mAh / g), initial charge / discharge efficiency (%), and battery capacity. (%), Self-discharge rate (% / month),
In many respects such as charge / discharge efficiency (%), the characteristics were inferior, and the secondary battery was not satisfactory in practical use.

It is speculated that this is because 1,3-dioxolane is polymerized on the negative electrode side (reduction side).

The present invention has been made in view of the above circumstances, and an object thereof is to provide a graphite having a large battery capacity, a small self-discharge rate, excellent cycle characteristics, and high charge-discharge efficiency. It is to provide a lithium secondary battery as a negative electrode material.

[0008]

In the first lithium secondary battery according to the present invention, in order to achieve the above object, a positive electrode containing a compound capable of occluding and releasing lithium as a main material, and an X-ray diffraction And a negative electrode mainly composed of graphite having a crystallite size Lc in the c-axis direction of 150 Å or more (excluding those having a crystallite size Lc in the c-axis direction in X-ray diffraction of less than 300 Å). A separator interposed between the positive and negative electrodes and an electrolytic solution in which an electrolyte solute is dissolved in a solvent, and the solvent is ethylene thiocarbonate , γ
-Thiobutyrolactone, γ-valerolactone, γ-ethyl-γ-butyrolactone, β-methyl-γ-butyrolactone , 3-methyltetrahydrofuran , 3-methylsulfolane, 2-methylsulfolane, 3-ethylsulfolane, At least one solvent selected from 2-ethylsulfolane, thiolane, α-pyrrolidone, pyrazolidine, pyrrolidine , 1,2-diethoxyethane and ethoxymethoxyethane was included.

Further, in the second lithium secondary battery according to the present invention, in order to achieve the above object, a positive electrode containing a compound capable of occluding and releasing lithium as a main material, and a c-axis direction in X-ray diffraction Between the positive electrode and the negative electrode whose main material is graphite having a crystallite size Lc of 150 Å or more (excluding those having a crystallite size Lc in the c-axis direction in X-ray diffraction of less than 300 Å). An interposed separator and an electrolytic solution in which an electrolyte solute is dissolved in a solvent are provided, and the solvent is ethylene carbonate alone or in addition to ethylene carbonate , ethylene thiocarbonate , γ-thiobutyrolactone, γ-valerolactone, γ-ethyl-γ-
Selected from butyrolactone, β-methyl-γ-butyrolactone, tetrahydrofuran, 3-methyltetrahydrofuran, sulfolane, 3-methylsulfolane, 2-methylsulfolane, 3-ethylsulfolane, 2-ethylsulfolane, thiolane, α-pyrrolidone, pyrazolidine, pyrrolidine It contains at least one solvent.

Here, in the first and second lithium secondary batteries of the present invention, the compounds capable of inserting and extracting lithium, which is the material of the positive electrode, are inorganic compounds such as Li ₂ FeO ₃ , TiO ₂ , and V. Examples thereof include oxides having so-called tunnel-shaped vacancies such as ₂ O ₅ and metal chalcogenides having a layered structure such as TiS ₂ and MoS _2.
i _x MO ₂ or Li _y M ₂ O ₄ (where M is a transition element, 0 ≦
x ≦ 1, 0 ≦ y ≦ 2) is preferable, and specific examples thereof include LiCoO ₂ and Li.
_{MnO 2, LiNiO 2, LiCrO 2} , LiMn 2 O 4 and the like.

Further, as an organic compound capable of inserting and extracting lithium as a material of the positive electrode, a conductive polymer such as polyaniline or a conductive polymer such as polyaniline is represented by the following perfluorocarbon sulfonic acid (manufactured by DuPont. Examples thereof include dopant-containing conductive polymers doped with the name “Nafion” or porphyrin.

[0012]

[Chemical 1]

In addition, as a compound capable of occluding and releasing lithium, which is a material of the positive electrode, LiCoO ₂ between graphite layers,
LiMnO ₂ , LiNiO ₂ , Li ₂ FeO ₃ , LiCrO
An intercalation compound in which a metal oxide such as ₂ is inserted, an intercalation compound in which an anion is inserted between graphite layers, an intercalation compound in which a halogen or a halide is inserted between graphite layers, and a porphyrin is inserted between graphite layers An intercalation compound or the like can also be used.

The above positive electrode material is kneaded with a conductive agent such as acetylene black or carbon black and a binder such as polytetrafluoroethylene (PTFE) or polyvinylidene difluoride (PVdF) to prepare a positive electrode mixture. Used as. Among the above-mentioned conductive polymers and dopant-containing conductive polymers, those having excellent conductivity may be kneaded with a binder without blending a conductive agent to obtain a positive electrode mixture.

Further, in the first and second lithium secondary batteries of the present invention, as the material of the negative electrode, graphite having a crystallite size Lc in the c-axis direction in X-ray diffraction of 150 Å or more as described above ( However, a carbon material containing a single component or a main component having a crystallite size Lc in the c-axis direction in X-ray diffraction of less than 300Å is used.

The above graphite has an average particle size of 1
In the range of ˜30 μm, the d value (d ₀₀₂ ) of the lattice plane (002) plane in X-ray diffraction is 3.35 to 3.40.
Graphite having a specific surface area of 0.5 to 50 m ² / within the range of Å
Graphite having a true density of 1.9 to 2.3 g / c
It is preferable to use graphite in the range of m ³ , further, the crystallite size La in the a-axis direction in X-ray diffraction is 150 Å or more, and the atomic ratio of H / C is 0.1 or less. Yes, G value in Raman analysis (1360 cm ^-1 / 1
It is more preferable to use graphite having 590 cm ⁻¹ of 0.05 or more.

The graphite as described above may be natural graphite, artificial graphite or quiche graphite. By the way, quiche graphite is used in a blast furnace at an iron mill.
When iron was melted at a temperature of 00 ° C or higher, the carbon contained in the iron sublimated, adhered to the furnace wall, and recrystallized. It is a high carbon material. Moreover, you may make it use the mixture of 2 or more types of these graphites as needed. The artificial graphite referred to here also includes graphite-based substances such as expanded graphite obtained by further processing and modifying graphite.

Examples of the above-mentioned natural graphite include graphite from Sri Lanka, graphite from Madagascar, flake graphite from Korea, soil graphite from Korea, and graphite from China, and artificial graphite includes coke-based graphite. The lattice plane (002) in X-ray diffraction of these natural graphite and artificial graphite
Table 1 shows the d value (d ₀₀₂ ) of the plane and the crystallite size Lc in the c-axis direction in X-ray diffraction.

[0019]

[Table 1]

Commercial products of the above natural graphite include
"NG-2", "NG-2L", "N" manufactured by Kansai Thermochemical Co., Inc.
"G-4", "NG-4L", "NG-7", "NG-7"
L "," NG-10 "," NG-10L "," NG-1 "
2 "," NG-12L "," NG-14 "," NG-1 "
4L "," NG-100 "," NG-100L "(above, high-purity graphite with a purity of 99% or more);" CX-3000 "," FBF "," BF "," CB "manufactured by Chuetsu Graphite Co., Ltd.
R ”,“ SSC-3000 ”,“ SSC-600 ”,
"SSC-3", "SSC", "CX-600", "C
"PF-8", "CPF-3", "CPB-6S", "C
PB "," 96E "," 96L "," 96L-3 ",
"90L-3", "CPC", "S-87", "K-"
3 "," CF-80 "," CF-48 "," CF-3 "
2 "," CP-150 "," CP-100 "," C
P "," HF-80 "," HF-48 "," HF-3 "
2 "," SC-120 "," SC-80 "," SC-6 "
0 "," SC-32 "(above, scaly graphite)," APF-
3000 "," APF "," AX-600 "," S- "
3 "," AP-6 "," AP-3 "," 300F ",
"150F" (above, soil graphite); "CSSP", "CSPE", "CSP", "special C" manufactured by Nippon Graphite Industry Co., Ltd.
P ”,“ CP ”,“ CP / B ”,“ CB-150 ”,
"CB-100", "F # 1", "F # 2", "F #
3 ”,“ SF • A ”,“ SF • B ”(above, scaly graphite),“ AOP ”,“ AUP ”,“ ASSP ”,“ AS ”
"P", "AP", "blue P", "APB", "PD",
"CA.C", "P # 1" (above, earth graphite), "AC
P-1000 "," ACP "," ACCB-150 ",
"SP-5", "SP-5L", "SP-10", "S"
P-10L "," SP-20 "," SP-20L ",
"SCB + 100", "SP-300", "HOP"
(The above is high-purity graphite having a purity of 97.5% or more).

Commercial products of the above-mentioned artificial graphite include
"RA-3000", "RA-15" manufactured by Chuetsu Graphite Co., Ltd.
"RA-44", "GX-600", "G-6S",
"G-3", "G-150", "G-100", "G-"
48 "," G-30 "," G-50 ";" HAG-150 "," HAG-15 "," HAG "manufactured by Nippon Graphite Industry Co., Ltd.
-5 "," PAG-15 "," PAG-5 "," PAG "
-80 "," PAG-60 "," SGS-100 ",
"SGS-50", "SGS-25", "SGS-1"
5 "," SGS-5 "," SGS-1 "," SGP-1 "
00 "," SGP-50 "," SGP-25 "," SG "
P-15 "," SGP-5 "," SGP-1 "," SG "
O-100 "," SGO-50 "," SGO-25 ",
"SGO-15", "SGO-5", "SGO-1",
"SGX-100", "SGX-50", "SGX-2"
5 "," SGX-15 "," SGX-5 "," SGX- "
1 ", 9QP% or more of high-purity artificial graphite," QP-2 "," QP-5 "," QP-10 ",
“QP-20” is exemplified.

Further, as a commercial product of artificial graphite obtained by further processing and modifying natural graphite, natural graphite powder is pitched,
"AOP-" manufactured by Nippon Graphite Industry Co., Ltd., which has been surface-treated with acrylic, titanate or the like to improve dispersibility in a resin.
Pi5 "," AOP-B5 "," AOP-A5 "," A
OP-T1 "is illustrated.

Further, as a commercially available product of expanded graphite obtained by expanding the layers of natural graphite by acid treatment, “S” manufactured by Chuetsu Graphite Co., Ltd.
"SLF", "SSMF", "SSFF", "SLF",
"SMF", "SFF", "EMK", "ELF",
"EMF", "EFF", "CMF";"EXP-SPM","EXP-12M","EX" manufactured by Nippon Graphite Industry Co., Ltd.
P-80M "and" EXP-SM "are illustrated.

Examples of graphite other than natural graphite and artificial graphite include the above-mentioned quiche graphite commercially available from Kansai Thermo Chemical Co., Inc., which may be used as the carbon material in the present invention.

The carbon material used in the present invention may be composed of only the above-mentioned graphite, or may be a material containing graphite as a main component and other carbon materials.

Here, as the carbon material containing graphite as a main component, for example, a mixture of graphite and a carbon material such as carbon black having a crystallite size Lc in the c-axis direction in X-ray diffraction of 8 Å or less, , A fired product of a mixture of graphite and pitch (both petroleum pitch and coal pitch can be used) having Lc of 150 Å or more. In the latter production, in order to obtain a calcined product having Lc of 150 Å or more, it is necessary to calcinate at a temperature of 1000 ° C or higher, and usually, the temperature is 1000 to 3000 ° C.

By thus adding carbon black or pitch to the graphite, the adhesion of the graphite to the core body (conductive substrate) can be improved. The preferred addition ratio of carbon black or pitch to graphite is in the range of 2 to 10 parts by weight of carbon black or pitch with respect to 100 parts by weight of graphite. This is because when the addition ratio of carbon black or pitch is less than 2 parts by weight, the above-mentioned effect of improving the adhesiveness is not sufficiently exhibited, while when the addition ratio exceeds 10 parts by weight, the energy density decreases, Furthermore, this is not preferable because it leads to a decrease in battery capacity.

The carbon material as described above is kneaded by a conventional method with a binder such as polytetrafluoroethylene or polyvinylidene difluoride to be used as a negative electrode mixture.

Further, in the present invention, as the graphite, the above expanded graphite or the like may be used instead of the powdery graphite, and the expanded graphite obtained by heat treatment and pressure molding may be used as the carbon material. Good.

Further, in the first lithium secondary battery according to the present invention, as a solvent in the electrolytic solution, ethylene thiocarbonate , γ-thiobutyrolactone, γ-valerolactone, γ-ethyl-γ-butyrolactone is used as described above. , Β-methyl-γ-butyrolactone , 3-methyltetrahydrofuran, sulfolane, 3-methylsulfolane, 2-methylsulfolane, 3-ethylsulfolane, 2
-At least one solvent selected from ethylsulfolane, thiolane, α-pyrrolidone, pyrazolidine, pyrrolidine , 1,2-diethoxyethane, and ethoxymethoxyethane.

Further, in the second lithium secondary battery according to the present invention, as a solvent in the electrolytic solution, ethylene thiocarbonate alone or ethylene thiocarbonate , γ- Thiobutyrolactone, γ-valerolactone, γ-ethyl-γ-butyrolactone, β-methyl-γ-butyrolactone, tetrahydrofuran, 3-methyltetrahydrofuran, sulfolane, 3-methylsulfolane, 2-methylsulfolane,
At least one solvent selected from 3-ethylsulfolane, 2-ethylsulfolane, thiolane, α-pyrrolidone, pyrazolidine, and pyrrolidine is contained.

Here, in the solvent shown in the above-mentioned first and second lithium secondary batteries, ethylene carbonate, ethylene thiocarbonate, γ-thiobutyrolactone, α-pyrrolidone and thiolane, which do not have a readily decomposable group, are used. , pyrazolidine, it is preferred to use pyrrolidine. That is, these solvents are propylene carbonate, 1,2-butylene carbonate, 2,3-butylene carbonate, γ-valerolactone, γ-ethyl-γ having a methyl group which is easily adsorbed on the active sites of graphite and decomposed. -Butyrolactone, β-methyl-γ-butyrolactone, dimethyl carbonate, diethyl carbonate,
Unlike a solvent such as 1,2-dimethoxyethane, 1,2-diethoxyethane, or ethoxymethoxyethane, it is stable in a redox atmosphere at the time of charging / discharging, does not generate a gas, and therefore does not generate lithium during charging. This is because the insertion of graphite into graphite is not hindered, and there is no polarization during charge / discharge due to gas overvoltage.

Further, in the first and second lithium secondary batteries of the present invention, not only one type of solvent is used as the solvent of the electrolytic solution as described above, but two or more types may be mixed if necessary. Can be used.

Here, as a suitable solvent, in addition to a solvent composed of ethylene carbonate, a mixed solvent composed of ethylene carbonate, γ-butyrolactone and sulfolane can be mentioned. Among them, ethylene carbonate is particularly preferable because it has a large battery capacity and high charge / discharge efficiency.

Here, in the case of a mixed solvent in which ethylene carbonate, γ-butyrolactone and sulfolane are mixed, a solvent containing 10% by volume or more of ethylene carbonate is preferable in that the battery capacity at high rate discharge is large.

Further, sulfolane (melting point: 28.9 ° C.) which is solid at room temperature is 1,2-dimethoxyethane (DME), 1,2-diethoxyethane (DEE), ethoxymethoxyethane (EME), etc. It is used by dissolving it in an ether low boiling point solvent, or an ester low boiling point solvent such as dimethyl carbonate (DMC) or diethyl carbonate (DEC). Even when a cyclic compound such as γ-butyrolactone that is liquid at room temperature is used, it is preferable to mix it with the above low boiling point solvent and use it as a mixed solvent in order to exhibit excellent low temperature characteristics.
In the present specification, the low boiling point solvent has a boiling point of 150.
The solvent at ° C or lower is designated.

When dimethyl carbonate is used as the low boiling point solvent among the mixed solvents obtained by mixing the low boiling point solvent as described above, the conductivity of dimethyl carbonate is high, and thus the high rate discharge characteristics are particularly improved. Further, when diethyl carbonate is used, the viscosity of diethyl carbonate at low temperatures is low and the ionic conductivity is excellent, so that the low-temperature discharge characteristics are particularly improved.

When the cyclic compound such as sulfolane is mixed with the low boiling point solvent, if the cyclic compound is contained in a proportion of 20 to 80% by volume, the battery capacity at high rate discharge is increased. Larger size is preferable.

In the first and second lithium secondary batteries of the present invention, examples of the electrolyte solute dissolved in the above-mentioned solvent include LiPF ₆ and LiB.
F ₄ , LiClO ₄ , LiCF ₃ SO ₃ , LiC ₄ F ₉ S
O ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiAsF ₆ or the like can be used. When dissolving such an electrolyte solute in the solvent as described above, the proportion of the electrolyte solute is preferably 0.1 to 3 mol / liter, more preferably 0.5 to 1.5 mol / liter. To liters.

The charge / discharge cycle characteristics of the lithium secondary battery using graphite satisfying the conditions of the present invention as the negative electrode material and the lithium secondary battery using coke which does not satisfy the conditions of the present invention as the negative electrode material are shown below. The investigation was conducted and the results are shown in FIG. Here, in FIG. 1, the vertical axis represents the negative electrode potential (V) with respect to the Li / Li ⁺ monopolar potential, and the horizontal axis represents the capacity (mAh / g) per 1 g of the carbon material (graphite or coke). It is a graph, and the charge / discharge cycle characteristics of the lithium secondary battery using graphite as the negative electrode material are shown by solid lines, and the charge / discharge cycle characteristics of the lithium secondary battery using coke as the negative electrode material are shown by broken lines. The direction of the arrow in the figure indicates the direction in which the negative electrode potential rises and falls during charging and discharging. The charge / discharge cycle characteristics shown in the drawing are data for both batteries when a mixed solvent of ethylene carbonate and dimethyl carbonate having a volume ratio of 1: 1 was used as an electrolytic solution solvent.

First, the charge / discharge cycle of a lithium secondary battery using coke as a negative electrode material will be described with reference to FIG. The potential of the negative electrode (point a), which was about 3 (V) before the initial charging, was Li / Li ⁺ single-pole potential (the negative electrode potential on the vertical axis is this as the initial charging progressed and Li was occluded in the coke). The electric potential approaches the reference (0 V), and when charging is completed, point b (negative electrode potential: 0 V, capacity: 30)
0 mAh / g). The coke at point b is brown to red. Next, when the first discharge is performed, the potential of the negative electrode rises as the discharge progresses, and the point c (capacity: 50 to 100 mA) indicating the discharge end potential (about 1 V).
h / g). During the first discharge, the hysteresis reaches the point c without returning to the route followed during the initial charge, because Li corresponding to the capacity shown by P in the figure is trapped in the coke, This is because in the subsequent electrode reaction in charge and discharge, only Li in an amount corresponding to the capacity indicated by Q in the figure can participate in the reaction. By repeating the subsequent charge and discharge cycles, the potential of the negative electrode is c → b → c → b ...
It fluctuates in a cycle like.

Next, the charging / discharging cycle in the lithium secondary battery using graphite as the negative electrode material will be described.
Before the initial charging, the potential of the negative electrode (a) was about 3 (V) as in a lithium secondary battery using coke as a negative electrode material.
The point is that as the initial charging progresses and Li is occluded in the graphite, it approaches the Li / Li + unipolar potential.
It reaches the point d (capacity: 375 mAh / g) at which the potential with respect to the Li / Li + single electrode potential is 0V. It should be noted that the graphite at point d had a golden color, which confirms that C ₆ Li was also produced by X-ray diffraction. Next, when the first discharge is performed, the potential of the negative electrode rises as the discharge progresses, and point e (capacity: 2) indicating the discharge end potential (about 1 V).
5 mAh / g). By repeating the subsequent charge / discharge cycle, the potential of the negative electrode fluctuates in a cycle such as e → d → e → d.

Based on the charge / discharge cycle characteristics shown in FIG.
Comparing the battery characteristics of a lithium secondary battery using graphite as a negative electrode material and a lithium secondary battery using coke as a negative electrode material, charging per 1 g of graphite at the time of initial charging in a lithium secondary battery using graphite as a negative electrode material Capacity is 375mA
While it is large at about h / g (point d), the charging capacity per 1 g of coke at the time of initial charging in a lithium secondary battery using coke as a negative electrode material is small at about 300 mAh / g (point b), and A lithium secondary battery using graphite as a negative electrode material has a large capacity per 1 g of graphite up to a discharge end potential of 1 V of about 350 mAh / g (de), whereas a lithium secondary battery using coke as a negative electrode material has a large capacity. The capacity per 1 g of coke up to the discharge end voltage of 1 V is 20
It is as small as about 0 to 250 mAh / g (bc).

This means that the charge / discharge efficiency of the lithium secondary battery using graphite as the negative electrode material is higher than that of the lithium secondary battery using coke as the negative electrode material.

The charging / discharging curve of the lithium secondary battery using graphite as the negative electrode material shows that during discharge from point d to point e
The negative electrode potential rises sharply near point e, which is almost flat, whereas the charge / discharge curve of the lithium secondary battery using coke as the negative electrode material gradually increases from point b to point c. There is.

This means that the lithium secondary battery using graphite as the negative electrode material is superior to the lithium secondary battery using coke as the negative electrode material in terms of discharge voltage flatness.

As compared with the lithium secondary battery using coke as the negative electrode material as described above, the lithium secondary battery using graphite as the negative electrode material has a higher charge / discharge efficiency and a flat discharge voltage. This means that the lithium secondary battery using graphite as the negative electrode material has a larger discharge capacity than the lithium secondary battery using coke as the negative electrode material.

[0048]

EXAMPLES The present invention will be described in more detail based on the following examples, but the invention is not intended to be limited by the examples described below, and various modifications may be made without departing from the scope of the invention. Is possible.

Reference Example 1 [Production of Positive Electrode] Cobalt carbonate and lithium carbonate were mixed at a Co: Li atomic ratio of 1: 1 and then heat-treated in air at 900 ° C. for 20 hours to obtain LiCoO ₂ . It was

LiC as the positive electrode material thus obtained
In oo ₂ , acetylene black as a conductive agent and a fluororesin dispersion as a binder were added in a weight ratio of 9
The mixture was mixed at a ratio of 0: 6: 4 to obtain a positive electrode mixture. And
This positive electrode mixture was rolled on an aluminum foil as a current collector and heat-treated under vacuum at 250 ° C. for 2 hours to produce a positive electrode.

[Preparation of Negative Electrode] Fluororesin dispersion as a binder was added to each of natural graphite, artificial graphite and Lonza graphite produced in China as a negative electrode material of 400 mesh pass in a weight ratio of 9
The mixture was mixed at a ratio of 5: 5 to obtain a negative electrode mixture. Then, each of these negative electrode mixtures was rolled on an aluminum foil serving as a current collector, and heat-treated under vacuum at 250 ° C. for 2 hours to produce negative electrodes containing each carbon material as a main material. here,
The particle size of graphite used for the negative electrode is preferably 400 mesh pass, and more preferably 2 to 14 μm.

Further, the above-mentioned natural graphite, artificial graphite and Lonza graphite produced in China all had a crystallite size Lc in the c-axis direction in X-ray diffraction of 300 Å or more.

Here, the X-ray diffraction was conducted under the following measurement conditions (the following X-ray diffraction was also conducted under the same measurement conditions). Source: CuKα Slit: Divergence slit 1 °, Scattering slit 1 °, Receiving slit 0.3 mm Gonio radius: 180 mm Graphite curved crystal monochromator

[Preparation of Electrolytic Solution] LiPF ₆ was dissolved at 1 mol / liter in a mixed solvent of ethylene carbonate and dimethyl carbonate at a volume ratio of 1: 1 to prepare an electrolytic solution. The mixing ratio is 0.00
The range of 1: 1 to 1: 0.01 is preferable.

[Production of Reference Batteries BA1 to BA3] A cylindrical non-aqueous electrolyte secondary battery was produced using the positive and negative electrodes and the electrolyte described above. The reference battery BA1 using natural graphite as the carbon material, the reference battery BA2 using artificial graphite, and the reference battery B using Lonza graphite.
It is represented by A3. As the separator, ion-permeable polypropylene (manufactured by Daicel, trade name "Duraguard") was used.

FIG. 2 is a cross-sectional view of the produced reference batteries BA1 to BA3. These reference batteries BA1 to BA3 include a positive electrode 1 and a negative electrode 2, a separator 3 for separating these electrodes, a positive electrode lead 4, and a negative electrode lead 5. , Positive electrode external terminal 6, negative electrode can 7 and the like. The positive electrode 1 and the negative electrode 2 are housed in the negative electrode can 7 in a spirally wound state via the separator 3 into which the electrolytic solution is injected, and the positive electrode 1 is connected to the positive electrode external terminal 6 via the positive electrode lead 4. Further, the negative electrode 2 is connected to the negative electrode can 7 through the negative electrode lead 5 so that the chemical energy generated inside the battery BA1 can be taken out as electric energy to the outside.

Comparative Example 1 Comparative battery BC1 was prepared in the same manner as in Reference Example 1 except that coke having Lc of 26Å was used as the negative electrode material.
Was produced.

(Charge / Discharge Characteristics of Each Battery) FIG. 3 shows the above reference batteries BA1 to BA3 and comparative battery B.
6 is a graph showing the charge and discharge characteristics of the C1 at 250 mA (constant current discharge) after the second cycle, with the voltage (V) on the vertical axis and the time (h) on the horizontal axis, and FIGS.
Are the charge and discharge characteristics of the reference battery BA1 and the reference battery BA2, respectively, compared with the charge and discharge characteristics of the comparative battery BC1, where the vertical axis represents the potential (V) of the negative electrode with respect to the Li / Li + single electrode potential. 6 is a graph in which the axis indicates charge / discharge capacity (mAh / g).

From these figures, the reference batteries BA1 to BA3 using the Chinese-made natural graphite, artificial graphite, and Lonza graphite as the negative electrode material are superior to the comparative battery BC1 using the coke as the negative electrode material in excellent charging / discharging. It is understood to have characteristics.

FIG. 6 shows the above reference batteries BA1 and BA.
2 is a graph showing the cycle characteristics of No. 2 and comparative battery BC1, with the vertical axis representing discharge capacity (mAh / g) and the horizontal axis representing cycle number. From the figure, reference battery cells BA1 and BA2 using Chinese-made natural graphite and artificial graphite as the negative electrode material are
Compared to the comparative battery BC1 using coke as the negative electrode material,
It can be seen that excellent cycle characteristics are exhibited.

The reference batteries BA1 to BA3 and the comparative battery BC1 were each charged and then stored at room temperature for 1 month, and the storage characteristics were measured. As a result, the self-discharge rate of the reference batteries BA1 to BA3 is 2 to 5% /
The month was 15% for the comparative battery BC1.

(Reference Example 2) As a negative electrode material, 1000 parts of a mixture prepared by adding 5 parts by weight of pitch to 100 parts by weight of the above-mentioned natural graphite produced in China was used.
A reference battery BA4 was produced in the same manner as in Example 1 except that the carbon material fired at a temperature of ° C was used. Here, the carbon material obtained as described above is
The crystallite size Lc in the c-axis direction in X-ray diffraction is 15
It was 0Å.

FIG. 7 is a graph showing the cycle characteristics of the above-mentioned reference battery BA4, with the vertical axis representing the battery discharge capacity (mAh / g) and the horizontal axis representing the number of cycles. Note that FIG.
For comparison, the cycle characteristics of a reference battery BA1 using only the above-mentioned natural graphite as a negative electrode material and a comparative battery BC1 using coke are also shown for comparison.

From the figure, the reference battery BA4 exhibits less cycle characteristics than the comparative battery BC1 using coke and the reference battery BA1 using only natural graphite because the carbon material is less likely to fall off the electrode. I know what to do.

Reference Example 3 As a negative electrode material, 5 parts by weight of carbon black having a crystallite size Lc of 8 Å in the c-axis direction in X-ray diffraction was added to 100 parts by weight of the above-mentioned natural graphite produced in China. A reference battery BA5 was produced in the same manner as in Reference Example 1 except that the above mixture was used.

FIG. 8 is a graph showing the cycle characteristics of the reference battery BA5 described above, with the vertical axis representing the discharge capacity (mAh / g) of the battery and the horizontal axis representing the number of cycles. Note that FIG.
For comparison, the cycle characteristics of a reference battery BA1 using only the above-mentioned natural graphite as a negative electrode material and a comparative battery BC1 using coke are also shown for comparison.

From the same figure, it can be seen that the reference battery BA5 exhibits less cycle characteristics than the comparative battery BC1 using coke and the reference battery BA1 using only natural graphite, because the carbon material is less likely to fall off the electrode. I know what to do.

Reference Example 4 Instead of a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) in a volume ratio of 1: 1 as a solvent for the electrolytic solution, in Reference Battery BA6, ethylene carbonate and diethyl carbonate (DEC) were used. ) And volume ratio 1:
1 in the comparative battery BC2, a mixed solvent of ethylene carbonate and dipropyl carbonate (DPC) in a volume ratio of 1: 1 and 1,3-dioxolane (1,3-DOL) in the conventional battery. A reference battery BA6, a comparative battery BC2 and a conventional battery were produced in the same manner as in Reference Example 1 except for the above.

FIG. 9 is a graph showing the charge / discharge characteristics of these batteries, with the vertical axis representing the negative electrode potential (V) and the horizontal axis representing the charge / discharge capacity.

From the figure, it can be seen that the reference battery BA6, like the reference battery BA1 described above, exhibits superior charge / discharge characteristics as compared with the comparative battery BC2 and the conventional battery.

Reference Example 5 d value (d ₀₀₂ ) of the lattice plane (002) plane in X-ray diffraction
Negative electrodes were manufactured using 13 kinds of carbon materials different from each other, and 13 kinds of batteries were manufactured in the same manner as in Reference Example 1 except for the above.

FIG. 10 is a graph showing the relationship between the d ₀₀₂ value of the carbon material and the discharge capacity of the battery. The discharge capacity (mAh / g) of the battery is plotted on the vertical axis, and the d of the carbon material used is d.
_{The 002} value (Å) is plotted on the horizontal axis.

From the figure, d ₀₀₂ is 3.35 to 3.40Å
It can be seen that the battery using graphite as a carbon material has a large discharge capacity.

Reference Example 6 Twelve kinds of batteries were prepared in the same manner as in Reference Example 1 except that a negative electrode was prepared using 12 kinds of carbon materials having different true densities.

FIG. 11 is a graph showing the relationship between the true density of the carbon material and the discharge capacity of the battery.
Ah / g) is plotted on the vertical axis, and the true density (g / cm ³ ) of the carbon material used is plotted on the horizontal axis.

From the figure, the true density is 1.9 to 2.3 g / c.
It can be seen that the battery using m ³ of graphite as the carbon material has a large discharge capacity.

Reference Example 7 Nine kinds of batteries were prepared in the same manner as in Reference Example 1 except that a negative electrode was prepared using 9 kinds of carbon materials having different average particle diameters.

FIG. 12 is a graph showing the relationship between the average particle size of the carbon material and the discharge capacity of the battery. The discharge capacity (mAh / g) of the battery is plotted on the ordinate and the average particle size of the carbon material used. (Μm) is shown on the horizontal axis.

From the figure, it is understood that the battery using graphite having an average particle diameter of 1 to 30 μm as the carbon material has a large discharge capacity.

Reference Example 8 13 kinds of batteries were prepared in the same manner as in Reference Example 1 except that a negative electrode was prepared using 13 kinds of carbon materials having different specific surface areas.

FIG. 13 is a graph showing the relationship between the specific surface area of the carbon material and the discharge capacity of the battery. The discharge capacity (mAh / g) of the battery is plotted on the vertical axis, and the specific surface area (m) of the carbon material used. ² / g) is a graph showing the horizontal axis.

From the figure, the specific surface area is 0.5 to 50 m ² /
It can be seen that the battery using the graphite of g as the carbon material has a large discharge capacity.

Reference Example 9 A negative electrode was prepared using 11 kinds of carbon materials having different crystallite sizes Lc in the c-axis direction in X-ray diffraction, and otherwise the same as in Reference Example 1 above. Eleven types of batteries were produced.

FIG. 14 is a graph showing the relationship between the Lc of the carbon material and the discharge capacity of the battery. The discharge capacity (mA) of the battery is shown in FIG.
h / g) on the vertical axis and Lc (Å) of the carbon material used
Is a graph in which the horizontal axis represents.

From the figure, Lc is 150 Å or more, especially 30
It can be seen that a battery using graphite having a volume of 0 Å or more as a negative electrode material has a large discharge capacity.

( Experimental Example 1) As an electrolytic solution, an electrolytic solution prepared by dissolving LiPF ₆ in a solvent shown in Tables 2 and 3 at a ratio of 1 mol / liter was used. Similarly, experiment
21 kinds of batteries according to the example were manufactured.

Then, the 21 kinds of batteries in Experimental Example 1 were discharged at 100 mA to obtain graphite characteristics [capacity per unit weight (mAh / g) and initial charge / discharge efficiency (%)] and battery characteristics [battery capacity (battery capacity mAh), self-discharge rate (% /
Month), cycle life (times), charge / discharge efficiency (%)], and the results are shown in Tables 2 and 3.

[0088]

[Table 2]

[0089]

[Table 3]

(Comparative Example 2) As an electrolytic solution, 1,3-dioxolane and 1 LiPF ₆ were added.
A conventional battery was prepared in the same manner as in Reference Example 1 except that the electrolyte solution was used at a mol / liter ratio. The conventional battery was also discharged at 100 mA as described above, and the same items as in Experimental Example 1 were measured, and the results are shown in Tables 2 and 3.

( Experimental Example 2) As an electrolytic solution, LiPF was added to the mixed solvent shown in Tables 4 and 5.
An electrolytic solution in which ₆ was dissolved at a ratio of 1 mol / liter was used, and otherwise the same as in Reference Example 1 above,
Twenty types of batteries according to the experimental example were manufactured. And this fruit
As for each battery in Experimental Example 2, 100
After discharging at mA, the same items as in Experimental Example 1 were measured, and the results are shown in Tables 4 and 5.

[0092]

[Table 4]

[0093]

[Table 5]

( Experimental example 3) As an electrolytic solution, LiPF was added to the mixed solvent shown in Tables 6 and 7.
An electrolytic solution in which ₆ was dissolved at a ratio of 1 mol / liter was used, and otherwise the same as in Reference Example 1 above,
Twenty types of batteries according to the experimental example were manufactured. And this fruit
As for each battery in Experimental Example 3, 100
After discharging with mA, the same items as in Experimental Example 1 were measured, and the results are shown in Tables 6 and 7.

[0095]

[Table 6]

[0096]

[Table 7]

( Experimental Example 4) As an electrolytic solution, LiPF 6 was added to the mixed solvent shown in Tables 8 and 9.
An electrolytic solution in which ₆ was dissolved at a ratio of 1 mol / liter was used, and otherwise the same as in Reference Example 1 above,
Twenty types of batteries according to the experimental example were manufactured. And this fruit
For each battery in Experimental Example 4, as described above, 100
After discharging at mA, the same items as in Experimental Example 1 above were measured, and the results are shown in Tables 8 and 9.

[0098]

[Table 8]

[0099]

[Table 9]

( Experimental Example 5) LiNiO ₂ was used as the positive electrode material, and
As shown in Tables 10 and 11, the same electrolytic solution as in the case of Experimental Example 1 was used, and other than that, in the same manner as in Reference Example 1 above, 21 types of batteries according to Experimental Examples were produced. Each battery in Experimental Example 5 was also discharged at 100 mA as described above, and the same items as in Experimental Example 1 were measured, and the results are shown in Tables 10 and 11.

[0101]

[Table 10]

[0102]

[Table 11]

Experimental Example 6 LiMn ₂ O ₄ was used as the positive electrode material, and
As shown in Tables 12 and 13, the same electrolytic solution as in the case of Experimental Example 1 was used, and other than that, in the same manner as in Reference Example 1 described above, 21 types of batteries according to Experimental Examples were produced. Each battery in Experimental Example 6 was also discharged at 100 mA as described above, and the same items as in Experimental Example 1 were measured, and the results are shown in Tables 12 and 13.

[0104]

[Table 12]

[0105]

[Table 13]

( Experimental Example 7) As an electrolytic solution, Li was added to a mixed solvent shown in Tables 14 and 15.
Five kinds of batteries according to Experimental Examples were produced in the same manner as in Reference Example 1 except that an electrolytic solution in which PF ₆ was dissolved at a rate of 1 mol / liter was used. And this
For each battery in Experimental Example 7, as described above,
After discharging at 0 mA, the same items as in Experimental Example 1 were measured and the results are shown in Tables 14 and 15.

[0107]

[Table 14]

[0108]

[Table 15]

From Tables 2 to 15 above, it is understood that the batteries according to the experimental examples of the present invention exhibit excellent battery characteristics in all the measured items as compared with the conventional battery.

( Experimental Example 8) As a solvent of the electrolytic solution, the volume mixing ratio of ethylene carbonate (EC) and γ-butyrolactone (γ-BL) was 1
00:00, 90:10, 80:20, 70:30, 6
0:40, 50:50, 40:60, 30:70, 2
Eleven kinds of solvents of 0:80, 10:90, and 0: 100 were used, and an electrolyte solution in which LiPF ₆ was dissolved in each solvent at a ratio of 1 mol / liter was used. In the same manner as in Example 1 , 11 types of batteries according to the experimental examples were manufactured. Then, for each battery in this Experimental Example 8, the battery capacity (mAh) was obtained by discharging at 100 mA,
The relationship between the volume mixing ratio (volume%) of ethylene carbonate and γ-butyrolactone and the battery capacity (mAh) was investigated, and the results are shown in the graph of FIG.

As a result, the battery capacity when discharged at 100 mA as described above was high in the battery using the solvent containing 10% by volume or more of ethylene carbonate.

( Experimental Example 9) As solvents for the electrolytic solution, ethylene carbonate (EC), γ-butyrolactone (γ-BL), and sulfolane (SL).
And the volume mixing ratio of 1: 0: 0, 90: 5: 5, 8
0:10:10, 70:15:15, 60: 20: 2
0, 50:25:25, 40:30:30, 30: 3
5:35, 20:40:40, 10:45:45, 0:
Using 11 kinds of solvents becomes 50:50, the electrolytic solution used, which obtained by dissolving LiPF ₆ to each solvent in a ratio of 1 mol / liter, and otherwise in the same manner as the above Reference Example 1, Experimental Example 11 kinds of batteries according to the present invention were produced. Then, with respect to each battery in Experimental Example 9, the battery capacity (mAh) was obtained by discharging at 100 mA, and the relationship between the volume mixing ratio (volume%) of ethylene carbonate, γ-butyrolactone and sulfolane and the battery capacity (mAh). Was examined and the results are shown in the graph of FIG.

As a result, the battery capacity when discharged at 100 mA as described above was high in the battery using the solvent containing 10% by volume or more of ethylene carbonate.

( Experimental Example 10) As a solvent of the electrolytic solution, a volume mixing ratio of tetrahydrofuran (THF) and dimethyl carbonate (DMC) was 1.
00:00, 90:10, 80:20, 70:30, 6
0:40, 50:50, 40:60, 30:70, 2
Eleven kinds of solvents having a ratio of 0:80, 10:90, and 0: 100 were used, an electrolytic solution in which LiPF ₆ was dissolved in each solvent at a ratio of 1 mol / liter was used, and LiNiO ₂ was used as a positive electrode material. Eleven kinds of batteries according to Experimental Examples were prepared in the same manner as in Reference Example 1 except for the above. And about each battery in this Experimental example 10,
The battery capacity (mAh) was obtained by discharging at 1 A, the relationship between the volume mixing ratio (volume%) of tetrahydrofuran and dimethyl carbonate and the battery capacity (mAh) was investigated, and the result is shown in the graph of FIG. 17.

As a result, the battery capacity when discharged at 1 A as described above was 20 to 8% tetrahydrofuran.
It was higher in the battery using the solvent contained in the range of 0% by volume.

( Experimental Example 11) As a solvent for the electrolytic solution, the volume mixing ratio of sulfolane (SL) and dimethyl carbonate (DMC) was 100: 0,
90:10, 80:20, 70:30, 60:40, 5
0:50, 40:60, 30:70, 20:80, 1
Eleven kinds of solvents having a ratio of 0:90 and 0: 100 were used, an electrolyte solution in which LiPF ₆ was dissolved in each solvent at a ratio of 1 mol / liter was used, and Li was used as a positive electrode material.
Eleven types of batteries according to experimental examples were manufactured in the same manner as in Reference Example 1 except that NiO ₂ was used. And
For each battery in Experimental Example 11, the battery capacity (mAh) was obtained by discharging at 1 A, and the volume mixing ratio (volume%) of sulfolane and dimethyl carbonate and the battery capacity (m
The relationship with Ah) was investigated, and the results are shown in the graph of FIG.

As a result, the battery capacity when discharged at 1 A as described above is 20 to 80% by volume of sulfolane.
It was higher in the battery using the solvent contained in the range.

In the above experimental example , a specific example in which the present invention is applied to a cylindrical battery is described. However, the shape of the battery is not particularly limited, and the present invention is applicable to various shapes such as prismatic and flat lithium batteries. It can be applied to a secondary battery.

[0119]

INDUSTRIAL APPLICABILITY The lithium secondary battery according to the present invention has a large battery capacity and a high charge / discharge efficiency.

[Brief description of drawings]

FIG. 1 is a graph showing charge / discharge cycle characteristics of reference batteries BA1 to BA3 and comparative battery BC1.

FIG. 2 is a cross-sectional view of a cylindrical battery.

FIG. 3 is a graph showing charge / discharge characteristics of reference batteries BA1 to BA3 and comparative battery BC1.

FIG. 4 is a graph showing charge / discharge characteristics of reference battery BA1.

FIG. 5 is a graph showing charge / discharge characteristics of reference battery BA2.

FIG. 6 is a graph showing cycle characteristics of reference batteries BA1 and BA2 and comparative battery BC1.

FIG. 7 is a graph showing charge / discharge characteristics of reference battery BA4.

FIG. 8 is a graph showing cycle characteristics of reference battery BA5.

FIG. 9 is a graph showing cycle characteristics of a reference battery BA6, a comparative battery BC2, and a conventional battery.

FIG. 10 is a graph showing the relationship between the d ₀₀₂ value of a carbon material and the discharge capacity of a battery.

FIG. 11 is a graph showing the relationship between the true density of a carbon material and the discharge capacity of a battery.

FIG. 12 is a graph showing the relationship between the average particle size of a carbon material and the discharge capacity of a battery.

FIG. 13 is a graph showing the relationship between the specific surface area of a carbon material and the discharge capacity of a battery.

FIG. 14 is a graph showing the relationship between the crystallite size Lc of the carbon material in the c-axis direction in X-ray diffraction and the discharge capacity of the battery.

FIG. 15 is a graph showing a relationship between a battery capacity and a solvent volume mixing ratio in Experimental Example 8 of the present invention.

FIG. 16 is a graph showing the relationship between the battery capacity and the solvent volume mixing ratio in Experimental Example 9 of the present invention.

FIG. 17 is a graph showing the relationship between the battery capacity and the solvent volume mixing ratio in Experimental Example 10 of the present invention.

FIG. 18 is a graph showing the relationship between the battery capacity and the solvent volume mixing ratio in Experimental Example 11 of the present invention.

[Explanation of symbols]

BA1 battery 1 positive electrode 2 Negative electrode 3 separator 4 Positive lead 5 Negative electrode lead 6 Positive external terminal 7 Negative electrode can

Front page continuation (72) Inventor Nobuhiro Furukawa 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Toshiyuki Noma 2-5-5 Keihan Hondori, Moriguchi City, Osaka Prefecture Sanyo Electric Co., Ltd. (72) Inventor Masatoshi Takahashi 2-5-5 Keihan Hondori, Moriguchi City, Osaka Sanyo Electric Co., Ltd. (56) Reference JP-A-4-337247 (JP, A) JP-A-5 -28996 (JP, A) JP 3-8270 (JP, A) JP 2-172162 (JP, A) JP 64-2258 (JP, A) JP 59-96666 (JP, A) ) JP-A-63-102166 (JP, A) JP-A-63-121260 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01M 10/40 H01M 4/02 H01M 4 / 58

Claims (14)

(57) [Claims] 1. A positive electrode containing a compound capable of occluding and releasing lithium as a main material, and graphite having a crystallite size Lc in the c-axis direction in X-ray diffraction of 150 Å or more (provided that the crystallite size in the c-axis direction in X-ray diffraction is A negative electrode having a crystallite size Lc of less than 300Å as a main material, a separator interposed between the positive and negative electrodes, and an electrolytic solution in which an electrolyte solute is dissolved in a solvent, As a solvent, ethylene thiocarbonate , γ-thiobutyrolactone, γ-valerolactone, γ-ethyl-γ-butyrolactone, β-methyl-γ
-Butyrolactone , 3-methyltetrahydrofuran , 3
-Methylsulfolane, 2-methylsulfolane, 3-ethylsulfolane, 2-ethylsulfolane, thiolane, α-
A lithium secondary battery comprising at least one solvent selected from pyrrolidone, pyrazolidine, pyrrolidine , 1,2-diethoxyethane, and ethoxymethoxyethane. 2. The solvent is ethylene thiocarbonate, γ-butyrolactone, γ-thiobutyrolactone, γ
-Valerolactone, γ-ethyl-γ-butyrolactone,
β-methyl-γ-butyrolactone, tetrahydrofuran, 3-methyltetrahydrofuran, sulfolane, 3-
A mixed solvent of dimethyl carbonate and a solvent selected from methylsulfolane, 2-methylsulfolane, 3-ethylsulfolane, 2-ethylsulfolane, thiolane, α-pyrrolidone, pyrazolidine, and pyrrolidine. The lithium secondary battery described in. 3. The solvent is ethylene thiocarbonate, γ-butyrolactone, γ-thiobutyrolactone, γ
-Valerolactone, γ-ethyl-γ-butyrolactone,
β-methyl-γ-butyrolactone, tetrahydrofuran, 3-methyltetrahydrofuran, sulfolane, 3-
2. A mixed solvent of diethyl carbonate and a solvent selected from methylsulfolane, 2-methylsulfolane, 3-ethylsulfolane, 2-ethylsulfolane, thiolane, α-pyrrolidone, pyrazolidine, and pyrrolidine. The lithium secondary battery described in. 4. The solvent is ethylene thiocarbonate , γ-thiobutyrolactone, γ-valerolactone, γ
-Ethyl-γ-butyrolactone, β-methyl-γ-butyrolactone, tetrahydrofuran, 3-methyltetrahydrofuran, sulfolane, 3-methylsulfolane, 2-
A mixed solvent of 1,2-dimethoxyethane and a solvent selected from methylsulfolane, 3-ethylsulfolane, 2-ethylsulfolane, thiolane, α-pyrrolidone, pyrazolidine and pyrrolidine. The lithium secondary battery described. 5. The solvent is dimethyl carbonate,
The lithium secondary battery according to claim 1, which is a mixed solvent of sulfolane and a solvent selected from diethyl carbonate, 1,2-diethoxyethane, and ethoxymethoxyethane. 6. The lithium secondary battery according to claim 1, wherein the solvent is a mixed solvent of tetrahydrofuran and dimethyl carbonate. 7. A positive electrode containing a compound capable of inserting and extracting lithium as a main material, and graphite having a crystallite size Lc in the c-axis direction in X-ray diffraction of 150 Å or more (provided that the crystallite size in the c-axis direction in X-ray diffraction is A negative electrode having a crystallite size Lc of less than 300Å as a main material, a separator interposed between the positive and negative electrodes, and an electrolytic solution in which an electrolyte solute is dissolved in a solvent, The solvent is ethylene carbonate alone, or in addition to ethylene carbonate , ethylene thiocarbonate , γ-thiobutyrolactone, γ-valerolactone, γ-ethyl-γ-butyrolactone, β-methyl-
γ-butyrolactone, tetrahydrofuran, 3-methyltetrahydrofuran, sulfolane, 3-methylsulfolane, 2-methylsulfolane, 3-ethylsulfolane, 2
A lithium secondary battery comprising at least one solvent selected from ethylsulfolane, thiolane, α-pyrrolidone, pyrazolidine and pyrrolidine. 8. The solvent is a mixed solvent of ethylene carbonate, sulfolane and γ-butyrolactone,
The lithium secondary battery according to claim 7, wherein the ratio of γ-butyrolactone is less than 50% by volume. 9. (00) in X-ray diffraction of said graphite
2) The lithium secondary battery according to any one of claims 1 to 8, wherein the d value of the surface is 3.35 to 3.40Å. 10. The (00
2) The lithium secondary battery according to any one of claims 1 to 8, wherein the d value of the plane is 3.354 to 3.365Å. 11. The graphite has an average particle size of 1 to 30 μm.
The lithium secondary battery according to any one of claims 1 to 10, wherein 12. The graphite has a specific surface area of 0.5 to 50.
The lithium secondary battery according to any one of claims 1 to 11, characterized in that the m ² / g. 13. The true density of the graphite is 1.9 to 2.3 g.
/ Cm < ³ >, The lithium secondary battery in any one of Claims 1-12 characterized by the above-mentioned. 14. The lithium secondary battery according to claim 1, wherein LiPF ₆ is dissolved as a solute in the electrolytic solution.